Combined Power And Communications Cable

ABSTRACT

Aspects of the present invention provide an improved cable having a reduced cross section while continuing to provide high voltage (noisy) power signals alongside low voltage (noise-susceptible) data signals. The improved cable can be used for power delivery and communications between a motor and a drive in an industrial control system. The reduced cross section advantageously improves handling. By providing separate groups between a group delivering the power signals and a group providing the data signals, thereby enforcing a physical separation, and by twisting together individual conductors of the group delivering the power signals with the group providing the data signals and the groups providing the separation, the reduced cross section can be achieved while continuing to minimize noise and interference onto the data signals due to the power signals.

CROSS-REFERENCE TO MATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.15/364,970, filed on. Nov. 30, 2016, entitled “Combined Power andCommunications Cable,” which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to combined power and communicationscables and, in particular, to combined power and communications cablingfor use in industrial control systems.

Industrial controllers are specialized computer systems used for thecontrol of industrial processes or machinery, for example, in a factoryenvironment. Industrial controllers typically control numerous modulesvia specialized control networks for accomplishing different tasks inthe industrial system. One such module may be a variable frequency drive(“VFD”) unit, which, in turn, may deliver power to, communicate withand/or control a motor. In industrial applications, motors may be usedto affect a variety of motions in the industrial process. For example,motors may be operated at continuous or variable speeds, such as forturning the blades of a fan or the rollers of an assembly line atconstant or variable speeds at different times, or may be used toprecisely control the position of objects and machines, such asprecisely controlling the movement of a robotic arm or the opening andclosing of a door.

Drive units typically have access to a power source and utilize atransistor network to deliver high voltage three phase electric power toa motor. Motors typically receive power from the drive unit and in turnfeed the power through electrical windings which surround a motor corewith one or more magnets, thereby electromagnetically powering themotor. Delivery of such power to the motor typically requirestransmission of significant amounts of power and energy, which isinherently a source of electrical interference and noise. As such, driveunits typically deliver such power via dedicated power cables tominimize electromagnetic interference (“EMI”).

Drive units also typically provide data communication and control overthe motor. Such data communication may be bi-directional between thedrive unit and the motor. For example, drive units may sendcommunications to the motor to turn the motor on, adjust the position,adjust the direction, adjust the speed, or apply a brake, such as duringan emergency. Drive units may also receive communications from themotor, such as for measuring the precise position of the motor, speed(revolutions per minute), temperature, or run-time.

Motors typically include encoders which may precisely measure (or sense)the position of the motor or which may communicate with one or moreother intelligent sensors or devices integrated with the motor, such asa temperature sensor or timer. The encoders may communicate suchinformation to the drive unit. Encoders may communicate information viaone or more digital data signals over a transmission line, which may befor example a single-ended line or a differential pair.

Communication transmission lines typically involve low voltageelectrical signals that are susceptible to electrical interference andnoise, which may thereby cause signal integrity loss and resulting dataloss. Consequently, drive units often communicate with motors viadedicated communications cables.

Many implementations require multiple cables for separate power deliveryand communications, thereby increasing the cost and complexity of thedesigns by automatically doubling the number of cables and connectorsthat are required. U.S. Pat. No. 9,018,529, assigned to the presentassignee, describes an approach in which power and communicationsconductors are combined in a single cable while minimizing one or moreof the aforementioned drawbacks. It is now desired to further improvethe aforementioned combined cable.

SUMMARY OF THE INVENTION

Aspects of the present invention provide an improved cable having areduced cross section while continuing to provide high voltage (noisy)power signals alongside low voltage (noise-susceptible) data signals.The improved cable can be used for power delivery and communicationsbetween a motor and a drive in an industrial control system. The reducedcross section advantageously improves handling. By providing separategroups between a group delivering the power signals and a groupproviding the data signals, thereby enforcing a physical separation, andby twisting together individual conductors of the group delivering thepower signals with the group providing the data signals and the groupsproviding the separation, the reduced cross section can be achievedwhile continuing to minimize noise and interference onto the datasignals due to the power signals.

Larger cable cross sections can present several drawbacks, such as:smaller bend radius; increased manufacturing costs for additionalmaterial usage; increased complexity for connectors; limitedavailability for connectors; limited availability of compatible units;and/or increased distortion of data signals. Moreover, by placing acommunication link in a same core and under a same electrical braid asnoisy power delivery conductors (which may be used, for example, toconnect switching Insulated-Gate Bipolar Transistors (“IGBT's”) formotor stator windings), the communication links can be increasinglysusceptible to signal distortion. Consequently, achieving good noiserejection with a reduced cable cross section is desirable.

As described herein, the present invention may provide an improved cableconfiguration by strategically placing conductors within a single cableto minimize crosstalk between high voltage, noisy power lines and lowvoltage communication subassembly, while achieving a smallest corefootprint possible. Aspects of the invention can include electricalshielding, jacketing, and/or use of fillers to further reduce electricalinterference. Locating three power delivery conductors close togetheralong an edge of an electrical screen can allow for controlled fieldconcentration within a cable core. A communication subassembly can thenbe located away from the concentrated field area in a quietest area ofthe cable. Power delivery conductors can utilize insulation materialwith a low dielectric constant for low capacitive coupling to minimizevoltage spikes at stator windings in a drive and to minimize cablelosses which can cause heating of the drive.

In one aspect, the cable can provide power delivery conductors alongsidesubassemblies which can include a communications subassembly and anoptional motor control brake subassembly. The motor control brakesubassembly could consist of, for example, two or more insulatedconductors which could be twisted around a common center. Aluminizedtape can optionally be applied to provide an electrical screen. Copperbraid can be applied over the twisted pair to provide the electricalscreen as well as safe separation of a low voltage circuit from a highvoltage circuit.

The communications subassembly can consist of two insulated conductorstwisted around a common center and covered by insulation of a lowdielectric constant to achieve low delay, high impedance and minimumsignal distortion. Filler can be used in valleys of the twisted pair foradded distance between conductors and a braided shield and tosubstantially maintain a round geometric shape. Tape wrap can also beused over both conductors and a filler to create a uniform core alongthe length of a cable. Aluminized tape can be optionally applied toprovide electrical screen for high frequency noise. Copper braid can beapplied over the twisted pair to provide an electrical screen as well assafe separation of a low voltage circuit from a high voltage circuit. Ajacket or tape can be used around the electrical braid for insulationand added support.

The communications subassembly can be separated from the power deliveryconductors by separation groups on opposing sides. One separation groupcould be the motor control brake subassembly. Another separation groupcould be a protective ground signal. The power delivery conductors, thecommunications subassembly and the separation groups can be twistedtogether around a common center which could be a solid filler having arounded cross-section, a fibrillated filler and/or a pliable filler andcan have a low dielectric. The twisted together groups can then becovered by one or more of a core wrap, an electrical screen or tape(such as aluminized tape), an electrical shield (such as a braidedcopper shield), a low friction tape (which can serve as a flex assist),and an extruded cable jacket.

Specifically then, one aspect of the present invention can provide acombined power and communications cable including: first, second andthird insulated conductors for delivering three phase electric power,the first, second and third insulated conductors forming a first group;fourth and fifth insulated conductors for providing data communication,the fourth and fifth insulated conductors being twisted together andcovered by an electrical shield, the fourth and fifth insulatedconductors forming a second group; and third and fourth groups havingrounded insulated cross-sections. The second group can be placed betweenthe third and fourth groups, and the third and fourth groups can each beplaced between the first and second groups around a common center. Also,the first, second, third and fourth groups can be twisted togetheraround the common center and covered by an electrical shield.

Another aspect can provide a method for combining power andcommunications in a cable including: providing first, second and thirdinsulated conductors for delivering three phase electric power, thefirst, second and third insulated conductors forming a first group;twisting together fourth and fifth insulated conductors for providingdata communication and covering the fourth and fifth insulatedconductors in an electrical shield, the fourth and fifth insulatedconductors forming a second group; providing third and fourth groupshaving rounded insulated cross-sections; placing the second groupbetween the third and fourth groups and the third and fourth groups eachbetween the first and second groups around a common center; and twistingtogether the first, second, third and fourth groups around the commoncenter and covering the first, second, third and fourth groups in anelectrical shield.

Another aspect can provide an industrial control system including: amotor powered by three phase electric power and having an encoder; adrive unit for delivering three phase electric power to the motor andfor communicating with the encoder; and a combined power andcommunications cable coupling the motor and the drive unit including:first, second and third insulated conductors for delivering the threephase electric power, the first, second and third insulated conductorsforming a first group; fourth and fifth insulated conductors forproviding data communication between the motor and the drive unit, thefourth and fifth insulated conductors being twisted together and coveredby an electrical shield, the fourth and fifth insulated conductorsforming a second group; and third and fourth groups having roundedinsulated cross-sections. The second group can be placed between thethird and fourth groups, and the third and fourth groups can each beplaced between the first and second groups around a common center. Thefirst, second, third and fourth groups can be twisted together aroundthe common center and covered by an electrical shield.

These and other objects, advantages and aspects of the invention willbecome apparent from the following description. The particular objectsand advantages described herein can apply to only some embodimentsfalling within the claims and thus do not define the scope of theinvention. In the description, reference is made to the accompanyingdrawings which form a part hereof, and in which there is shown apreferred embodiment of the invention. Such embodiment does notnecessarily represent the full scope of the invention and reference ismade, therefore, to the claims herein for interpreting the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplar industrial control system with acombined power and communications cable for use with a motor and a driveunit in accordance with an aspect of the invention;

FIG. 2 is a cross-sectional view of a combined power and communicationscable which can be used in the system of FIG. 1 in accordance with anaspect of the invention;

FIG. 3 is a cross-sectional view of a communications subassembly of thecable of FIG. 2;

FIG. 4 is a cross-sectional view of an optional motor control brakesubassembly of the cable of FIG. 2; and

FIG. 5 is an isometric view of the combined power and communicationscable of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

One or more specific embodiments of the present invention will bedescribed below. It is specifically intended that the present inventionnot be limited to the embodiments and illustrations contained herein,but include modified forms of those embodiments including portions ofthe embodiments and combinations of elements of different embodiments ascome within the scope of the following claims. It should be appreciatedthat in the development of any such actual implementation, as in anyengineering or design project, numerous implementation-specificdecisions must be made to achieve the developers' specific goals, suchas compliance with system-related and business related constraints,which may vary from one implementation to another. Moreover, it shouldbe appreciated that such a development effort might be complex and timeconsuming, but would nevertheless be a routine undertaking of design,fabrication, and manufacture for those of ordinary skill having thebenefit of this disclosure. Nothing in this application is consideredcritical or essential to the present invention unless explicitlyindicated as being “critical” or “essential.”

Referring now to the drawings wherein like reference numbers correspondto similar components throughout the several views and, specifically,referring to FIG. 1, the present invention shall be described in thecontext of an exemplar industrial control system 10. The industrialcontrol system 10 may include a programmable logic controller (“PLC”) 12with a locally accessible Human Machine Interface (“HMI”) or computerterminal 14 having a keyboard, mouse and a display. The PLC 12 cancommunicate via a control network with a variable frequency drive(“VFD”) unit 16. The drive unit 16 has access to a power source andutilizes a transistor network (not shown) to deliver three phaseelectric power to a motor 20 via a combined power and communicationscable 22. The drive unit 16 also bi-directionally communicates data withthe motor 20 via cable 22.

The cable 22 includes first, second and third insulated conductors 24,26 and 28, respectively, for delivering the three phase electric powerto the motor 20. The cable 22 also includes fourth and fifth insulatedconductors 30 and 32, respectively, for low voltage (lower than thefirst, second and third insulated conductors 24, 26 and 28,respectively) data communications with the motor 20. The cable 22 alsoincludes a sixth insulated conductor 34 for delivering a protectiveground to the motor 20. The cable 22 may also optionally include seventhand eighth insulated conductors 36 and 38, respectively, for additionalcontrol over the motor 20. The cable 22 can connect to the drive unit 16at a single drive unit connector 40, and connects to the motor 20 at asingle motor connector 42, thereby electrically and mechanicallycoupling the drive unit 16 to the motor 20. In another aspect, multiplecables 22 can be connected serially with connectors in between (notshown).

The motor 20 can comprise a stator with electrical windings 44 which areplaced around a rotor 46 with magnets. The motor 20, receiving the powerfrom the drive unit 16, feeds the power into the electrical windings 44,which, in turn, electromagnetically interacts with the rotor 46 withmagnets, creating a mechanical force to thereby rotate the motor. As aresult, the rotor 46 rotates a shaft 48, which can affect a variety ofmotions in the industrial process (not shown). Depending on how power isapplied to the electrical windings 44, the shaft 48 can be moved andstopped at precise positions, in clockwise or counter-clockwisedirections, and can be moved at continuous or varying speeds.

The motor 20 can also comprise an encoder 50 which can precisely measure(or sense) position of the shaft 48 via a detection plate 52, or whichcan communicate with one or more other intelligent sensors or devices 54integrated within the motor, such as one or more temperature sensorsand/or timers. The encoder 50 can then communicate such information tothe drive unit 16 via the fourth and fifth insulated conductors 30 and32. The encoder 50 can also receive communications from the drive unit16 via the fourth and fifth insulated conductors 30 and 32 to effectsuch operations as the motor can be configured to allow. In analternative aspect, the motor 20 can include additional signalconditioning and/or logic, for example, which can act on the electricalpower delivery to the motor for exercising control over such aspects asprecisely moving the motor in either direction.

The motor 20 can also optionally comprise a solenoid actuated brake 58,which is attached to shaft 48 and is designed to lock in place whencontrolled to do so, allowing for motor service and braking. Thesolenoid actuated brake 58 can receive a low voltage (lower than thefirst, second and third insulated conductors 24, 26 and 28,respectively, for delivering the three phase electric power)communication trot the drive unit 16 via the seventh and eighthinsulated conductors 36 and 38, respectively to apply a brake to stopthe motor, such as during an emergency.

Referring now to FIGS. 2 and 5, cross-sectional and isometric views,respectively, of the cable 22 are shown in accordance with an aspect ofthe invention. The first, second and third insulated conductors 24, 26and 28, respectively, for delivering three phase electric power andhaving high voltage relative to the communications signals are providedin a first group 60 (a power delivery group). The low voltage fourth andfifth insulated conductors 30 and 32, respectively, for datacommunication are separately provided in a second group 62 (a datacommunications group) (see FIG. 3). Each insulated conductor cancomprise, for example, a copper conductor core surrounded by anelectrically insulating jacket having a low dielectric constant.

Third and fourth groups 64 and 66 (separation groups), respectively, areplaced on opposing sides of the second group 62 (the data communicationsgroup). Accordingly, one separation group (such as the third group 64)is placed between the second group 62 (the data communications group)and the first group 60 (the power delivery group) on one side; andanother separation group (such as the fourth group 66) is placed betweenthe second group 62 (the data communications group) and the first group60 (the power delivery group) on an opposing side, around a commoncenter 68. The third and fourth groups 64 and 66 (separation groups),respectively, can have rounded insulated cross-sections, and the thirdand fourth groups 64 and 66 groups, respectively, can each preferablyinclude at least one insulated conductor. In one aspect, the third group64 can comprise a sixth insulated conductor for delivering a protectiveground, and the fourth group 66 can comprise seventh and eighthinsulated conductors 36 and 38, respectively, for providing motor brakecontrol (optional motor control brake subassembly) (see FIG. 4). Thefirst, second, third and fourth groups 60, 62, 64 and 66, respectively,can then be twisted together around the common center 68. The commoncenter 68 can be a solid filler having a rounded cross-section, thoughin alternative aspects, the common center can be a fibrillated and/orpliable material and can have a low dielectric.

In one aspect, the fourth and fifth insulated conductors 30 and 32,respectively, in the second group 62, providing low voltagecommunication signals, can each have a greater wire gauge than any ofthe first, second and third insulated conductors 24, 26 and 28,respectively, in the first group 60, delivering the three phase electricpower. Moreover, the fourth and fifth insulated conductors 30 and 32,respectively, can each have a greater wire gauge than any of the seventhand eighth insulated conductors 36 and 38, respectively, in the fourthgroup 66, providing motor brake control. The sixth insulated conductorin the third group 64, delivering the protective ground, can have a wiregauge equivalent to any of the first, second and third insulatedconductors 24, 26 and 28, respectively, in the first group 60. In apreferred aspect, the fourth and fifth insulated conductors 30 and 32,respectively, in the second group 62 can have an American Wire Gauge(AWG) rating of 22 or more, and the first, second and third insulatedconductors 24, 26 and 28, respectively, in the first group 60, and thesixth insulated conductor in the third group 64, can each have an AWGrating of 18 or less.

The twisted together first, second, third and fourth groups 60, 62, 64and 66, respectively, can be covered in one or more layers to achievevarious effects. In one aspect, the first, second, third and fourthgroups 60, 62, 64 and 66, respectively, can be covered by a core wrap70, which can be, for example, a Polyester or Polypropylene (PP) tape,Nylon binder or similar material allowing some flexibility and movementof the first, second, third and fourth groups 60, 62, 64 and 66,respectively. The core wrap 70 can optionally contain filler (notshown), such as PP, for substantially maintaining a round geometricshape of the cable 22. The core wrap 70, in turn, can be covered by ametallic tape 72 or foil (electrical screen), which can be aluminized,so as to attenuate high frequency electrical noise. The metallic tape 72can be applied in a manner so as to provide sufficient overlap resultingin complete coverage. The metallic tape 72, in turn, can be covered byan electrical shield 74. The electrical shield 74 can be a braidedcopper shield used to minimize Electromagnetic Interference (EMI). Theelectrical shield 74, in turn, can be covered by a low friction tape 76(flex assist) which can allow movement between the inner cable body anda cable jacket. The low friction tape 76, in turn, can be covered by acable jacket 78, which can be, for example, a Thermoplastic Elastomer(TPE) or Polyvinylchloride (PVC) material extruded over the cable corefor protecting the cable 22. The material and thickness of the cablejacket 78 can be determined by regulatory demands and can providephysical protection from the elements and improved durability. It willbe appreciated that the above ordering of the one or more layers can bevaried, and that certain layers can be excluded while other layers areincluded, to achieve various effects as desired.

With additional reference to FIG. 3, the fourth and fifth insulatedconductors 30 and 32, respectively, forming the second group 62 for datacommunication (communications subassembly), are twisted together arounda common center and can also be covered by one or more communicationssubassembly layers to achieve various effects. By way of example, ashighlighted in FIG. 3, the fourth insulated conductor 30, like otherinsulated conductors in the cable 22, can include a conductor portion 30a, which can be copper, and an electrical insulator portion 30 bsurrounding the conductor portion 30 a. In one aspect, the fourth andfifth insulated conductors 30 and 32, respectively, can be covered by atape wrap 80 with a filler 82 contained beneath the tape wrap 80. Thefiller 82, which can be PP for example, can be applied for substantiallymaintaining the round geometric shape of the twisted fourth and fifthinsulated conductors 30 and 32, respectively, thereby further minimizingnoise and interference onto the communication signals by ensuringimproved impedance matching to electronics in the encoder and in thedrive unit. The filler 82 essentially fills the valleys that result fromtwisting together the fourth and fifth insulated conductors 30 and 32,respectively. The density of the filler 82 can be controlled to ensureoverall roundness of the twisted, shielded insulated conductors, whichresults in improved transmission line characteristics. The tape wrap 80,in turn, can be covered by a metallic tape 84 or foil (electricalscreen), which can be aluminized, so as to attenuate high frequencyelectrical noise. The metallic tape 84 can be applied in a manner so asto provide sufficient overlap resulting in complete coverage. Themetallic tape 84, in turn, can be covered by an electrical shield 86.The electrical shield 86 can be a braided copper shield used to minimizeEMI. The electrical shield 86, in turn, can be covered by a cable jacket88, which can be, for example, a TPE or PVC material extruded over thecommunications subassembly core for protecting the second group 62. Itwill be appreciated that the above ordering of the one or morecommunications subassembly layers can be varied, and that certain layerscan be excluded while other layers are included, to achieve variouseffects as desired.

With additional reference to FIG. 4, the fourth group 66 can compriseseventh and eighth insulated conductors 36 and 38, respectively, forproviding motor brake control (optional motor control brakesubassembly). The seventh and eighth insulated conductors 36 and 38,respectively, can be twisted together around a common center and can becovered by one or more motor control brake subassembly layers to achievevarious effects. By way of example, as highlighted in FIG. 4, theseventh insulated conductor 36, like other insulated conductors in thecable 22, can include a conductor portion 36 a, which can be copper, andan electrical insulator portion 36 b surrounding the conductor portion36 a. In one aspect, the seventh and eighth insulated conductors 36 and38, respectively, can be covered by a metallic tape 90 or foil(electrical screen), which can be aluminized, so as to attenuate highfrequency electrical noise. The metallic tape 90 can be applied in amanner so as to provide sufficient overlap resulting in completecoverage. The metallic tape 90, in turn, can be covered by an electricalshield 92. The electrical shield 92 can be a braided copper shield usedto minimize EMI. The electrical shield 92, in turn, can be covered by atape wrap 94 for containing the motor control brake subassembly. Thefourth group 66, as twisted together, can project through the cable 22in a round geometric shape. It will be appreciated that the aboveordering of the one or more motor control brake subassembly layers canbe varied, and that certain layers can be excluded while other layersare included, to achieve various effects as desired.

Accordingly, the cable 22 can have a reduced cross section whileproviding high voltage (noisy) power signals via the first, second andthird insulated conductors 24, 26 and 28, respectively, for deliveringthree phase electric power in the first group 60, alongside low voltage(noise-susceptible) data signals, via the fourth and fifth insulatedconductors 30 and 32, respectively, for data communication in the secondgroup 62. The reduced cross section advantageously improves handling. Byproviding the third and fourth groups 64 and 66, respectively, asseparation groups between the first group 60 delivering power and thesecond group 62 providing communications, thereby enforcing a physicalseparation, and by twisting together individual conductors of the firstgroup 60 delivering the power with the second group 62 providing thecommunications and the third and fourth groups 64 and 66, respectively,providing the separation, the reduced cross section can be achievedwhile continuing to minimize noise and interference onto the datasignals of the second group 62 due to the power signals of the firstgroup 60.

Certain terminology is used herein for purposes of reference only, andthus is not intended to be limiting. For example, terms such as “upper,”“lower,” “above,” and “below” refer to directions in the drawings towhich reference is made. Terms such as “front,” “back,” “rear,”“bottom,” “side,” “left” and “right” describe the orientation ofportions of the component within a consistent but arbitrary frame ofreference which is made clear by reference to the text and theassociated drawings describing the component under discussion. Suchterminology may include the words specifically mentioned above,derivatives thereof, and words of similar import. Similarly, the terms“first,” “second” and other such numerical terms referring to structuresdo not imply a sequence or order unless clearly indicated by thecontext.

When introducing elements or features of the present disclosure and theexemplary embodiments, the articles “a,” “an,” “the” and “said” areintended to mean that there are one or more of such elements orfeatures. The terms “comprising,” “including” and “having” are intendedto be inclusive and mean that there may be additional elements orfeatures other than those specifically noted. It is further to beunderstood that the method steps, processes, and operations describedherein are not to be construed as necessarily requiring theirperformance in the particular order discussed or illustrated, unlessspecifically identified as an order of performance. It is also to beunderstood that additional or alternative steps may be employed.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein and the claims shouldbe understood to include modified forms of those embodiments includingportions of the embodiments and combinations of elements of differentembodiments as coming within the scope of the following claims. All ofthe publications described herein including patents and non-patentpublications are hereby incorporated herein by reference in theirentireties.

What is claimed is:
 1. An electrical cable comprising: a plurality ofinsulated power conductors for delivering electric power; at least oneinsulated data conductor for providing data communication; and first andsecond separation structures, wherein the power conductors, the dataconductor and the separation structures are twisted together around acommon center and covered by an electrical shield, and wherein the firstseparation structure is arranged between the data conductor and thepower conductors on a first side of the power conductors and the secondseparation structure is arranged between the data conductor and thepower conductors on a second side of the power conductors.
 2. The cableof claim 1, wherein power conductors comprise first, second and thirdpower conductors for delivering three phase electric power.
 3. The cableof claim 1, wherein the electrical shield is a first electrical shieldand the data conductor is a first data conductor, and further comprisinga second data conductor, wherein the first and second data conductorsare twisted together and covered by a second electrical shield.
 4. Thecable of claim 1, wherein the first separation structure comprises aninsulated ground conductor for delivering a protective ground.
 5. Thecable of claim 4, wherein the second separation structure comprises atleast one insulated control conductor for providing motor control. 6.The cable of claim 5, wherein the electrical shield is a firstelectrical shield and the control conductor is a first controlconductor, and further comprising a second control conductor, whereinthe first and second control conductors are twisted together and coveredby a second electrical shield.
 7. The cable of claim 1, wherein thecommon center is a filler to maintain a round shape.
 8. The cable ofclaim 1, wherein the separation structures each have roundedcross-sections.
 9. The cable of claim 1, wherein the electrical shieldis a braided shield, and further comprising the power conductors, thedata conductor and the separation structures being covered by a metallictape interior to the braided shield.
 10. The cable of claim 9, furthercomprising the braided shield being covered by a cable jacket.
 11. Thecable of claim 10, further comprising a low friction tape between thebraided shield and the cable jacket.
 12. The cable of claim 1, whereinthe data conductor as a smaller cross section and the power conductorseach have a larger cross section.
 13. A method for combining power andcommunications in an electrical cable, the method comprising: providinga plurality of insulated power conductors for delivering electric power;providing at least one insulated data conductor for providing datacommunication; providing first and second separation structures;twisting together the power conductors, the data conductor and theseparation structures around a common center, wherein the firstseparation structure is arranged between the data conductor and thepower conductors on a first side of the power conductors and the secondseparation structure is arranged between the data conductor and thepower conductors on a second side of the power conductors; and coveringthe power conductors, the data conductor and the separation structuresby an electrical shield.
 14. The method of claim 13, wherein theelectrical shield is a first electrical shield and the data conductor isa first data conductor, and further comprising twisting together thefirst data conductor and a second data conductor and covering the firstand second data conductors by a second electrical shield.
 15. The methodof claim 13, wherein the electrical shield is a braided shield, andfurther comprising the power conductors, the data conductor and theseparation structures being covered by a metallic tape interior to thebraided shield.
 16. The method of claim 13, wherein the common centerand the separation structures each have rounded cross-sections.
 17. Themethod of claim 13, wherein the data conductor has a smaller crosssection and the power conductors each have a larger cross section. 18.An industrial control system comprising: a motor powered by multi-phaseelectric power and having an encoder; a drive unit for deliveringmulti-phase electric power to the motor and for communicating with theencoder; and a combined power and communications cable coupling themotor and the drive unit, comprising: first, second and third insulatedpower conductors for delivering the multi-phase electric power; at leastone insulated data conductor for providing data communication; and firstand second separation structures, wherein the power conductors, the dataconductor and the separation structures are twisted together around acommon center and covered by an electrical shield, and wherein the firstseparation structure is arranged between the data conductor and thepower conductors on a first side of the power conductors and the secondseparation structure is arranged between the data conductor and thepower conductors on a second side of the power conductors.
 19. Theindustrial control system of claim 18, wherein the electrical shield isa first electrical shield and the data conductor is a first dataconductor, and further comprising a second data conductor, wherein thefirst and second data conductors are twisted together and covered by asecond electrical shield.
 20. The industrial control system of claim 19,wherein a separation structure comprises at least one insulated controlconductor for providing brake control for the motor.